They are normally made of either asphalt or concrete. I can't recall which, but I have seen major airports with main runways made of asphalt. To the other question, the additional 1600 feet does make a difference. One, a hot summer day at DEN is 80-90, where as a hot summer day at LAS is 115. That evens them out some. Also, adding that extra usable runway means that you can run the plane longer down without as much danger of running out of pavement. Take, for example, when they tow out to JFK's 14k runway, airlines like Cathay probably use 12k feet. So, at DEN, they will use 14k feet, which would be scary at LAS or JFK. In a message dated 6/26/2003 3:48:02 PM Pacific Daylight Time, yul@xxxxxxxxxxx writes: << This brings up an interesting point with respect to construction. What are runways composed of? If you noticed, on the taxing out to the active, you'll see the active is being "scored" every few inches or greater. I would think asphalt, but there must be more to it. Anyone in airport inspection or construction have any insight here >>